feat(kernel): SEA-via-kernel PuPr tail: advanced proxy, Geography, conn/error telemetry, token-caching docs, configurable backoff

KERNEL_REV

@@ -1 +1 @@
-4d301455f7e70de9cb747e0f1143b8a3df8c5b48
+f29957733c8f6d79a7212bc8a50cf4e5ffa8dd69

connector.go

@@ -45,14 +45,16 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 	if c.cfg.UseKernel {
 		be, err = newKernelBackend(ctx, c.cfg)
 	} else {
-		// The experimental WithKernel* TLS options have no Thrift-path equivalent —
-		// reject them loudly rather than silently ignore, so a caller who sets a
-		// trusted-CA bundle / an independent hostname skip and forgets WithUseKernel
-		// learns the option had no effect instead of connecting with a
-		// weaker-than-intended (or unconfigured) TLS trust store.
+		// The experimental WithKernel* options have no Thrift-path equivalent — reject
+		// them loudly rather than silently ignore, so a caller who sets one (a
+		// trusted-CA bundle, a hostname-verify skip, a proxy, a retry budget, or a
+		// CloudFetch chunk cap) and forgets WithUseKernel learns the option had no
+		// effect instead of connecting as if it were never set. Every WithKernel*
+		// option allocates KernelExperimental, so this one gate covers them all; the
+		// message names the family rather than a stale subset that drifts as options
+		// are added.
 		if c.cfg.KernelExperimental != nil {
-			return nil, fmt.Errorf("databricks: a WithKernel* option "+
-				"(WithKernelTrustedCerts / WithKernelSkipHostnameVerify) %w; "+
+			return nil, fmt.Errorf("databricks: a WithKernel* option %w; "+
 				"add WithUseKernel(true) or remove it", dbsqlerr.ErrRequiresKernelBackend)
 		}
 		be, err = thrift.New(ctx, c.cfg, c.client)
@@ -97,6 +99,15 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 	if conn.telemetry != nil {
 		log.Debug().Msg("telemetry initialized for connection")
 		conn.telemetry.RecordOperation(ctx, conn.id, "", telemetry.OperationTypeCreateSession, sessionLatencyMs, nil)
+		// Connection-configuration telemetry on the kernel path only, so the
+		// default (Thrift) path's emitted telemetry stays byte-identical (the
+		// Thrift path has never populated DriverConnectionParameters). Emits mode /
+		// auth mech+flow / proxy / arrow / query-tags / metric-view for the
+		// just-opened session. Gated on the kernel backend, not just WithUseKernel,
+		// so it never fires when the kernel wasn't actually selected.
+		if _, ok := be.(*thrift.Backend); !ok {
+			conn.telemetry.RecordConnectionConfig(ctx, conn.id, kernelConnectionTelemetry(c.cfg))
+		}
 	}
 
 	// ServerProtocolVersion is Thrift-specific (not on the neutral backend
@@ -603,3 +614,85 @@ func WithKernelSkipHostnameVerify() ConnOption {
 		kernelExperimental(c).TLSSkipHostnameVerify = true
 	}
 }
+
+// KernelProxy is the explicit-proxy configuration for WithKernelProxy. Its fields
+// are named so a call site can't transpose the credentials — the four values are
+// all strings, so a positional signature would let a Username/Password swap (or a
+// misplaced BypassHosts) compile cleanly and fail only at runtime with wrong proxy
+// credentials.
+type KernelProxy struct {
+	// URL is the proxy URL (e.g. "http://proxy.internal:3128"). Required; empty is a
+	// no-op, leaving the environment-derived proxy (if any) in effect.
+	URL string
+	// Username / Password are optional out-of-band basic-auth credentials, supplied
+	// here rather than embedded in the URL userinfo. Empty means unset.
+	Username string
+	Password string
+	// BypassHosts is an optional comma-separated no-proxy host list. NO_PROXY is
+	// consumed during environment resolution and not forwarded to the kernel, so this
+	// is the only way to give the kernel a structured bypass list. Empty means unset.
+	BypassHosts string
+}
+
+// WithKernelProxy configures an explicit HTTP proxy for the kernel backend, with
+// optional out-of-band basic-auth credentials and a comma-separated bypass
+// (no-proxy) host list. It overrides the HTTP(S)_PROXY / NO_PROXY environment the
+// kernel path otherwise mirrors from the Thrift path.
+//
+// Use this instead of the proxy environment when you need the "advanced" fields
+// the env-var path can't express: a structured bypass list (NO_PROXY is consumed
+// during environment resolution, not forwarded to the kernel) or basic-auth
+// credentials supplied out of band rather than embedded in the URL userinfo.
+// KernelProxy.Username / Password / BypassHosts may be empty (passed to the kernel
+// as NULL, i.e. unset). An empty KernelProxy.URL is a no-op — the environment-derived
+// proxy, if any, stays in effect. A malformed URL is rejected at connect
+// (errors.Is ErrInvalidKernelConfig).
+//
+// An explicit WithKernelProxy takes precedence over the environment: consulting
+// both would be ambiguous, and an explicit proxy is a deliberate override.
+//
+// EXPERIMENTAL, kernel-only: the default (Thrift) backend rejects this at connect.
+func WithKernelProxy(p KernelProxy) ConnOption {
+	return func(c *config.Config) {
+		ke := kernelExperimental(c)
+		ke.ProxyURL = p.URL
+		ke.ProxyUsername = p.Username
+		ke.ProxyPassword = p.Password
+		ke.ProxyBypassHosts = p.BypassHosts
+	}
+}
+
+// WithKernelRetryOverallTimeout sets the cumulative retry budget across all
+// attempts on the kernel backend — the total time the kernel may spend retrying a
+// single logical request before giving up. This is the 4th retry knob, alongside
+// the backoff bounds and max attempts carried by the backend-neutral WithRetries
+// (RetryWaitMin / RetryWaitMax / RetryMax, which the kernel path also honors).
+//
+// It is a kernel-only option because the Thrift-path WithRetries surface has no
+// overall-budget equivalent; it mirrors the pyo3/napi retry_overall_timeout knob.
+// Zero (the default) keeps the kernel's built-in budget (900s).
+//
+// EXPERIMENTAL, kernel-only: the default (Thrift) backend rejects this at connect.
+func WithKernelRetryOverallTimeout(d time.Duration) ConnOption {
+	return func(c *config.Config) {
+		kernelExperimental(c).RetryOverallTimeout = d
+	}
+}
+
+// WithKernelMaxChunksInMemory bounds how many decompressed CloudFetch chunks the
+// kernel holds in memory at once on the kernel backend — the knob that trades
+// large-result throughput for peak RSS. Lower it (e.g. 4) to cap memory on wide,
+// row-heavy result sets; raise it for more download parallelism at higher memory.
+// A value <= 0 (the default) leaves the kernel's built-in default (16) in place.
+//
+// It is forwarded as the kernel's client-only "cloudfetch_max_chunks_in_memory"
+// session conf, which the kernel applies to its result config and strips before
+// the SEA wire — so it never reaches the server.
+//
+// EXPERIMENTAL, kernel-only: the default (Thrift) backend has no in-memory-chunk
+// knob and rejects this at connect.
+func WithKernelMaxChunksInMemory(n int) ConnOption {
+	return func(c *config.Config) {
+		kernelExperimental(c).MaxChunksInMemory = n
+	}
+}

doc.go

@@ -214,13 +214,14 @@ via the authType=oauthU2M DSN param); reading scalar, nested, and complex-typed
 results (CloudFetch is transparent); bound query parameters (positional and named);
 context cancellation during execute; the initial namespace (WithInitialNamespace,
 applied post-connect via USE CATALOG / USE SCHEMA); metric-view metadata
-(WithEnableMetricViewMetadata); and the TLS, proxy, and session-conf (query tags,
-statement timeout, time zone) options. Nothing is silently ignored: WithTimeout, a
-retries-disabling WithRetries, token-provider / external / federated
-authenticators, and custom M2M OAuth scopes (the kernel applies its own) are
-rejected at connect; staging (PUT/GET/REMOVE on a Unity Catalog volume) is
-rejected at execute. WithMaxRows and positive-limit WithRetries are
-accepted but inert (the kernel manages fetching and retries below the C ABI).
+(WithEnableMetricViewMetadata); the retry / backoff policy (WithRetries:
+RetryWaitMin / RetryWaitMax / RetryMax, including the disable form, forwarded to the
+kernel's HTTP retry config); and the TLS, proxy, and session-conf (query tags,
+statement timeout, time zone) options. Nothing is silently ignored: WithTimeout,
+token-provider / external / federated authenticators, and custom M2M OAuth scopes
+(the kernel applies its own) are rejected at connect; staging (PUT/GET/REMOVE on a
+Unity Catalog volume) is rejected at execute. WithMaxRows is accepted but inert (the
+kernel manages fetching below the C ABI).
 
 OAuth U2M is interactive: on a cache miss, connecting launches the system browser and
 blocks until login completes or the kernel's ~120s callback timeout expires. Because
@@ -233,30 +234,61 @@ backend exposes a U2M-scopes option, so this is a fixed difference between the t
 default sets, not a dropped setting; both authorize against the built-in public
 client.
 
-Experimental kernel-only TLS options (rejected by the default backend; the
+Experimental kernel-only options (rejected by the default backend; the
 WithKernel* prefix marks them experimental):
   - WithKernelTrustedCerts(pem) adds a PEM CA bundle on top of the system roots (for
     a re-signing proxy or on-prem CA). Required because the kernel's TLS stack does
     not read SSL_CERT_FILE.
   - WithKernelSkipHostnameVerify() skips only the hostname check while keeping chain
     validation (finer-grained than WithSkipTLSHostVerify).
-
-Setting either without WithUseKernel fails Connect with an error wrapping the
+  - WithKernelProxy(KernelProxy{URL, Username, Password, BypassHosts}) sets an explicit
+    HTTP proxy, overriding the HTTP(S)_PROXY / NO_PROXY environment the kernel path
+    otherwise mirrors. The fields are named (not positional) so the four same-typed
+    strings can't be transposed at the call site. Use it for the advanced fields the
+    env-var path can't express: a structured bypass (no-proxy) list, or basic-auth
+    credentials supplied out of band rather than embedded in the URL. An explicit proxy
+    takes precedence over the environment; empty credentials / bypass are passed to the
+    kernel as unset, and a malformed URL is rejected at connect.
+  - WithKernelRetryOverallTimeout(d) sets the cumulative retry budget across all
+    attempts — the 4th retry knob, alongside the backoff bounds and max attempts
+    carried by the backend-neutral WithRetries (also honored on the kernel path). It
+    is kernel-only because the Thrift WithRetries surface has no overall-budget
+    equivalent; it mirrors the pyo3/napi retry_overall_timeout knob. Zero keeps the
+    kernel's default budget (900s).
+  - WithKernelMaxChunksInMemory(n) bounds how many decompressed CloudFetch chunks the
+    kernel holds in memory at once — the knob that trades large-result download
+    throughput for peak RSS. Lower it (e.g. 4) to cap memory on wide, row-heavy result
+    sets; raise it for more parallelism at higher memory. It is forwarded as the
+    kernel's client-only cloudfetch_max_chunks_in_memory session conf, stripped before
+    the SEA wire so it never reaches the server. A value <= 0 keeps the kernel's
+    default (16).
+
+Setting any of these without WithUseKernel fails Connect with an error wrapping the
 sentinel ErrRequiresKernelBackend, detectable with errors.Is.
 
 Features above the backend seam are inherited unchanged: the database/sql connection
 pool, per-connection telemetry (CREATE_SESSION / EXECUTE_STATEMENT / DELETE_SESSION),
-and the telemetry circuit breaker. Result types render byte-for-byte identical to the
+and the telemetry circuit breaker. The kernel path additionally emits a
+connection-configuration telemetry event at connect (mode=SEA, auth mechanism/flow,
+proxy usage, arrow, query tags, metric-view metadata); this is kernel-only, so the
+default (Thrift) path's telemetry is unchanged. Result types render byte-for-byte identical to the
 Thrift backend: scalars, DECIMAL (exact string), TIMESTAMP / TIMESTAMP_NTZ (shifted
 into the session time zone), INTERVAL, nested Array/Map/Struct and VARIANT (as JSON),
-and GEOMETRY (WKT). The server query id is surfaced on the success path, so a
+and GEOMETRY / GEOGRAPHY (WKT). The server query id is surfaced on the success path, so a
 QueryIdCallback (see below) fires with the real id and EXECUTE_STATEMENT telemetry
 carries it.
 
 On the read path, context cancellation is honored at result-batch boundaries, not
 mid-fetch: an in-flight CloudFetch batch runs to completion before the cancel takes
 effect.
 
+OAuth token caching and HTTP client reuse are inherited from the kernel and need no
+driver configuration: the kernel caches U2M tokens on disk
+(~/.config/databricks-sql-kernel/oauth/, with refresh-token lifecycle) and M2M
+tokens in-memory with background refresh, and reuses a single pooled HTTP client per
+session across the control-plane, CloudFetch, and auth-refresh calls. There is no
+driver-side cache or pool knob because these live below the C ABI.
+
 # Programmatically Retrieving Connection and Query Id
 
 Use the driverctx package under driverctx/ctx.go to add callbacks to the query context to receive the connection id and query id.

errors/errors.go

@@ -82,6 +82,15 @@ var ErrKernelNotCompiled error = errors.New("the SEA-via-kernel backend is not c
 // the case programmatically instead of matching on message text.
 var ErrRequiresKernelBackend error = errors.New("requires the SEA-via-kernel backend")
 
+// value to be used with errors.Is() to determine that a kernel-backend option was
+// itself malformed (e.g. a WithKernelProxy URL that does not parse) — as opposed to
+// unsupported (ErrNotSupportedByKernel) or a transient connect failure. The kernel
+// path validates such options in the Go layer before handing them to the kernel's C
+// ABI, where the failure would otherwise surface as an opaque wrapped string a
+// caller can't branch on. Lets a caller distinguish "fix your config" from a
+// retryable error instead of matching on message text.
+var ErrInvalidKernelConfig error = errors.New("invalid kernel backend configuration")
+
 // Base interface for driver errors
 type DBError interface {
 	// Descriptive message describing the error